Novel perfluoroalkyl vinyl ether compound, process for preparing copolymer by using the compound, and optical plastic materials comprising copolymer prepared by the process

ABSTRACT

Disclosed herein are a novel perfluoroalkyl vinyl ether compound, a process for preparing a copolymer by using the perfluoroalkyl vinyl ether compound, and an optical plastic material comprising a copolymer prepared by the process. More specifically, the perfluoroalkyl vinyl ether has a particular molecular structure; the process is performed by copolymerizing the perfluoroalkyl vinyl ether compound with a common fluorinated olefin in the presence of a perfluorinated radical initiator; and, the optical plastic material comprises a copolymer prepared by the process and optionally a dopant. 
     The copolymerization of the perfluoroalkyl vinyl ether with a common fluorinated olefin can provide a copolymer having a high molecular weight. In addition, appropriate control of the composition of the monomers can provide a completely amorphous copolymer. Since the polymer prepared by the process exhibits excellent thermal properties and is substantially transparent in the UV and near IR regions, it can be usefully applied to various optical plastic materials. Furthermore, a preform for a GI type plastic optical fiber fabricated by using the copolymer and the dopant has a high T g , thus being stable, and a parabolic refractive index profile due to the presence of the dopant.

This non-provisional application claims priority under 35U.S.C. § 119(a)to Korean Patent Application No. 2004-529 filed on Jan. 6, 2004, whichis herein incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a novel perfluoroalkyl vinyl ethercompound, a process for preparing a copolymer by using theperfluoroalkyl vinyl ether compound, and an optical plastic materialcomprising a copolymer prepared by the process. More particularly, thepresent invention relates to a cyclic perfluoroalkyl vinyl ether havinga particular molecular structure, a process for preparing a copolymer bycopolymerizing the perfluoroalkyl vinyl ether compound with a commonfluorinated olefin in the presence of a perfluorinated radicalinitiator, and an optical plastic material comprising a copolymerprepared by the process, and optionally a dopant.

2. Description of the Related Art

In recent years, a number of optical plastic materials have been used asmedia for light transmission in the field of automobiles, OA machinesand various sensors. For example, plastic optical fibers (POFs) arewidely used as optical fibers for short-distance communication in placeof quartz glass. Plastic optical fibers are largely classified intograded refractive index (GI) type POFs and stepped refractive index (SI)type POFs. Generally, methylmethacrylate, styrene, carbonate, norborneneresins and the like are used as cores or clads of optical fibers. Theseresins are polymers having C—H bonds in their molecular structure. Whenthe polymer materials are used as materials for optical fibers,stretching or deformation vibration takes place due to the presence ofhydrogen atoms in the C—H bonds. As a result, the polymer materialsabsorb light of a characteristic wavelength corresponding to thevibration and light transmittance is therefore decreased. This is a maincause of optical loss. For instance, polymethylmethacrylate is evaluatedto have a theoretical absorption loss of 105 dB/km for a 650 nm lightsource and 10,000 dB/km for a 1,300 nm light source, due to C—H bondscontained in the compound.

It has been found that when the hydrogen atoms in the polymers arereplaced with fluorine atoms, no absorption loss substantially takesplace for a 650 nm light source and a theoretical absorption loss isonly about 1 dB/km between sixth and seventh overtones of the C—F bondsfor a 1,300 nm light source. For this reason, extensive research hasbeen undertaken on the use of fluorine polymers having C—F bonds asmaterials for optical fibers.

For example, Japanese Patent Laid-open No. Hei 8-334634 disclosespoly(heptafluoro-1-butene-trifluoro-vinylether) (hereinafter, referredto as ‘PBVE’), as a completely fluorinated optical plastic material,represented by the following formula:

This polymer is prepared by homopolymerizingperfluoro-(2,2-dimethyl-1,3-dioxole) having an allyl cyclic structurecontaining fluorine atoms in the main chain of the monomer, orcopolymerizing the monomer with tetrafluoroethylene orhexafluoropropylene.

Since the polymer PBVE is prepared from the monomer having an allylcyclic structure containing fluorine atoms in the main chain, itcontains no C—H bonds. In addition, it is known that PBVE has anamorphous structure and a T_(g) of 108° C. Further, the polymer PBVE iscommercially available under the brand name of “CYTOP” from Asahi GlassCo., Japan.

In addition to PBVE, Asahi Glass Co. proposed fluorinated polymers asmaterials for a GI (graded index) plastic optical fiber, represented bythe following formulae:

wherein l is a number of 0 to 5, m is a number of 0 to 4, n is a numberof 0 to 1, and 1+m+n is a number of 1 to 6; o, p and q are eachindependently a number of 0 to 5, and o+p+q is a number of 1 to 6; R, R₁and R₂ are each independently F or CF₃; and X₁ and X₂ are eachindependently F or Cl.

In order to produce POFs, particularly GI type POFs having a refractiveindex gradient using the above perfluorinated polymers, the use ofdopants is required (e.g., low molecular weight compounds or highmolecular weight compounds of oligomers or higher polymers containing noC—H bonds in their molecular structure). Additional requirements for thedopants are excellent compatibility with host polymers and a refractiveindex difference from the host polymers above a predetermined level.Many low molecular weight dopants are known, for example, halogenatedaromatic hydrocarbons containing no C—H bonds. Among these hydrocarbons,halogenated aromatic hydrocarbons containing only fluorine atoms ashalogen atoms and halogenated aromatic hydrocarbons containing fluorineatoms and other halogen atoms are preferred in terms of highcompatibility with host polymers. As high molecular weight or oligomericdopants, perfluorinated polymers having a refractive index differentfrom host polymers are known, for example, perfluorinated polymerscontaining only fluorine atoms as halogen atoms, and perfluorinatedpolymers containing fluorine atoms and other halogen atoms.

The production of GI type POFs using a perfluorinated polymer such asCYTOP is achieved by first fabricating a preform for a plastic opticalfiber (POF) having a refractive index gradient in a polymer by using adopant, followed by thermal drawing. At this time, the fabrication ofthe preform is possible by various methods (see, e.g., Japanese PatentNos. 10-268146 and Japanese Patent Laid-open No, Hei 8-334534): Forexample,

1) A perfluorinated polymer is melted; a dopant or a perfluorinatedpolymer containing the dopant is fed into the central portion of themolten polymer; and, the dopant is diffused so as to be molded into apreform.

2) A perfluorinated polymer prepared by melt-spinning; drawing is usedto form a central rod; and a dopant or a perfluorinated polymercontaining the dopant is repeatedly dip-coated onto the rod.

3) A hallow is formed in a perfluorinated polymer using a rotating glasstube; a dopant or a perfluorinated polymer containing the dopant isfilled into the perfluorinated polymer tube; and, the resultingstructure is rotated at a low speed.

4) A homogeneous mixture of a perfluorinated polymer and a dopant—or amixture obtained by uniformly mixing the perfluorinated polymer and thedopant in a solvent and evaporating the solvent only—is thermally drawnor melt-extruded to produce a fiber; and, the fiber is contacted with aninert gas under heating to form a refractive index gradient.

5) A rod or fiber consisting of a perfluorinated polymer is formed; adopant having a refractive index lower than the perfluorinated polymeror a perfluorinated polymer containing the dopant is coated on the rodor fiber; and, the coated structure is heated to diffuse the dopant,thereby forming a refractive index gradient.

6) A high refractive index polymer and a low refractive index polymer atvarious mixing proportions are heat-melted or mixed in a solvent; andthe obtained mixtures are diffused by extruding in a multilayer, therebyproducing a fiber having a refractive index gradient.

7) A stepped or multi-stepped preform is fabricated using aperfluorinated polymer and a dopant, and the dopant is diffused at theinterface between the steps to produce a GI type optical fiber.

In accordance with the above-mentioned methods, Asahi Glass Co., Japanand professor Koike developed GI type POF (commercial name: “Lucina”)having excellent optical properties at the level of an attenuation of 80dB/km and a bandwidth of 3 Gbps/100 m. It was developed so as to applyto office LAN and optical interconnection. “Lucina” exhibits a very lowoptical loss, a large transmission capacity at various wavelengths, andexcellent moisture resistance. However, the present inventors have foundproblems with “Lucina” in that the optical properties are non-uniformalong the length of the fiber, and the dopant used to control therefractive index gradient acts as a plasticizer. This greatlydeteriorates the thermal properties of the base resin, damaging thelong-term reliability. Particularly, the refractive index gradient isdeformed, decreasing the transmission capacity.

Accordingly, prior art perfluorinated polymers are not suitable toproduce POFs for access networks, office networks, automobiles, militarypurposes and aircraft, which require excellent heat resistance andlong-term reliability. When a dopant such as CTFE(chlorotrifluoroethylene) is combined with “CYTOP”, a non-crystalline,completely fluorinated homopolymer having a T_(g) of about 108° C., toproduce a plastic optical fiber, it functions to greatly lower the T_(g)of the host polymer. This combination of the dopant and CYTOP reducesthe T_(g) of the final POF to less than 90° C. Since the reduction inT_(g) decreases time and temperature stability, the use of “CYTOP” islimited in its application to POFs.

Examples of other fluorine-based polymers include Teflon AF (Dupont), acopolymer of 2,2-bistrifluoromethyl-4,5-difluoro-1,3-dioxole andtetrafluoroethylene, represented by the following formula:

wherein n is a real number of 1 or less.

However, according to a report by the International Plastic OpticalFiber Conference (2001), Teflon AF was reported to have a high opticalloss.

In order to effectively produce rod lenses, optical waveguides, opticaldecouplers, wavelength multiplexers and wavelength demultiplexers,optical attenuators, optical switches, optical isolators, lighttransmitting modules, light receiving modules, couplers, opticaldetectors and optical integrated circuits as well as POFs, using opticalplastic materials, the optical plastic materials must possess thefollowing properties: they must not exhibit light scattering; they mustbe substantially transparent over a very broad range of wavelengths;and, they must be excellent in various physiochemical propertiesincluding heat resistance. No optical materials satisfying theserequirements have hitherto been reported.

There is therefore a need in the art for an optical plastic materialthat exhibits the following properties: little or no light scattering;substantially transparent in the UV (wavelength: 200˜400 nm) and near IR(wavelength: 2,500 nm or shorter) regions; excellent heat resistance,therefore being stable even in the presence of a dopant; and, excellentchemical resistance, moisture resistance and flame retardancy.

The present inventors have earnestly and intensively conducted researchto develop an optical plastic material satisfying the above-mentionedrequirements. As a result, the present inventors have found that apolymer prepared by the copolymerization of a cyclic perfluoroalkylvinyl ether having a particular molecular structure and a perfluorinatedolefin monomer (for example, tetrafluoroethylene) in a chlorofluorinatedorganic solvent in the presence of a perfluorinated radical initiatorhas the following properties: it is substantially transparent in the UVand near IR regions; it has little or no optical loss upon lightpenetration; it has excellent heat resistance, chemical resistance,moisture resistance and compatibility with conventional dopants; and, itmaintains excellent heat resistance even in the presence of a dopant.The refractive index gradient formed by a dopant in the polymer is notdeformed despite time passage and varying temperatures and is stablymaintained. The present invention is based on these findings.

SUMMARY OF THE INVENTION

Therefore, it is a feature of the present invention to provide a polymersuitable for use in producing an optical plastic material that exhibitsthe following properties: little or no light scattering and optical lossupon light penetration; substantially transparent at the overallwavelengths; excellent heat resistance, thus being stable even in thepresence of a dopant; and, excellent chemical resistance, moistureresistance and flame retardancy.

It is another feature of the present invention to provide an opticalplastic material comprising the polymer.

In accordance with the features of the present invention, there isprovided a cyclic perfluoroalkyl vinyl ether compound having aparticular molecular structure.

In accordance with the features of the present invention, there isfurther provided a process for preparing a fluorinated polymer bycopolymerizing the perfluoroalkyl vinyl ether compound and aperfluorinated olefin monomer in a chlorofluorinated solvent in thepresence of a perfluorinated radical initiator.

In accordance with the features of the present invention, there isfurther provided a polymer prepared by the process.

In accordance with the features of the present invention, there isfurther provided an optical plastic material comprising the polymer, andoptionally a dopant having a refractive index different from thepolymer.

In accordance with the features of the present invention, there isfurther provided a preform for a plastic optical fiber fabricated fromthe optical plastic material.

In accordance with the features of the present invention, there is yetfurther provided a plastic optical fiber produced from the preform.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIGS. 1 and 2 are views schematically showing the structures ofpolymerization devices usable for the preparation of a polymer inaccordance with a preferred embodiment of the present invention; and

FIG. 3 is a graph showing the refractive index gradient of a preform fora GI type plastic optical fiber according to a preferred embodiment ofthe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the present invention will be explained in more detail withreference to the accompanying drawings.

A cyclic perfluoroalkyl vinyl ether according to the present inventionis represented by Formula 1 below:

wherein RF is a fluorine atom or a C_(1˜5) perfluoroalkyl group; A is asingle bond, —(CF₂)_(n)— (in which n is an integer of 1 to 5) or—(CF₂CR^(F) ₂—O—CF₂)— (in which substituents R^(F) are eachindependently a fluorine atom or a C₁₅ perfluoroalkyl group);

is a perfluoro cyclohexyl, perfluorophenyl, perfluorodioxanyl orperfluorodioxalanyl group.

More preferably, the cyclic perfluoroalkyl vinyl ether of the presentinvention is a compound represented by any one of Formulae 2 to 4 below:

These compounds can be prepared through appropriate pathways by knownsynthetic processes. For example, the compound of Formula 2 can beprepared by Reaction Scheme 1 below:

The compound of Formula 4 can be prepared by Reaction Scheme 2 below:

wherein HMPA is hexamethylphosphorictriamide ([(CH₃)₂N]₃P═O)].

The present invention additionally provides a process for preparing afluorinated polymer by copolymerizing the cyclic perfluoroalkyl vinylether and a perfluorinated olefin monomer in a chlorofluorinated solventin the presence of a perfluorinated radical initiator; and a polymerprepared by the process.

The perfluorinated olefin monomer is preferably a C_(2˜10)perfluorinated olefin monomer, and more preferably tetrafluoroethylene(hereinafter, referred to as ‘TFE’) or hexafluoropropylene. The molarratio of the cyclic perfluoroalkyl vinyl ether of Formula 1 to theperfluorinated olefin monomer is between 99:1 and 50:50. If thetetrafluoroethylene monomer is used in an amount exceeding 50 mole %,the final polymer has poor amorphousness and heat resistance.

Another fluorinated monomer that can be used in the process of thepresent invention is represented by Formula 5 below:

wherein R^(F) is a fluorine atom or a C_(1˜5) perfluoroalkyl group; and

is a perfluoro cyclohexyl, perfluorophenyl, perfluorodioxanyl orperfluorodioxalanyl group.

The perfluorinated radical initiator which can be used in the process ofthe present invention is preferably a perfluorinated peroxide compound.More preferred radical initiators includebis-perfluorocyclohexylperoxide of Formula 6 below, apolyperfluoroperoxide represented by Formula 7 below and mixturesthereof:

wherein n is an integer between 1 and 10, and m is an integer between 1and 40.

The molar ratio between the initiator and the total monomers may besuitably selected according to the desired molecular weight of the finalpolymer and the composition of the monomers. The molar ratio of thetotal monomers to the initiator is preferably controlled within10:1˜500:1.

The use of the compound of Formula 6 or 7 or a mixture thereof as theinitiator is advantageous over the use of conventional initiators interms of a) good hydrolytic stability in water media, b) a highpolymerization rate of the fluorinated monomers at 45˜75° C. and c)introduction of a heat resistant terminal group into the polymer.

The polymerization method is not particularly limited. Emulsionpolymerization is preferred in that the molecular weight of the polymercan be easily increased to desired levels. On the other hand, one canuse chlorofluorinated solvent as a polymerization solvent, preferably1,2-dichloro-1,1,2,2-tetrafluoroethane.

The polymerization temperature is preferably between 25 and 80° C., butis not particularly limited to this range.

Polymethacrylate has been used as a material for a POF. Sincepolymethacrylate contains a number of C—H bonds in its chains,stretching or deformation vibration takes place due to the presence ofhydrogen atoms in the C—H bonds upon light penetration. As a result, thepolymer absorbs light of a particular wavelength and light transmittanceis accordingly decreased, which is a main cause of optical loss. Thatis, when light is irradiated on a material containing C—H bonds, thematerial absorbs light of a characteristic wavelength corresponding tostretching or resonance vibration of the interatomic bonds.

Accordingly, the material containing C—H bonds is not suitable for usein plastic optical fibers for long-distance communication using light inthe near-IR region (600-1550 nm). In order to solve the above problemsof the prior art material, the present inventors developed a polymercontaining no C—H bonds in the molecular structure. No optical losstherefore takes place by light absorption even at long wavelengths aswell as at short wavelengths. The perfluorinated polymer prepared usingthe cyclic perfluoroalkyl vinyl ether of the present invention can besuitably used as a light transmission medium for optical devices. Lightranging from UV (ultraviolet) (i.e. at wavelengths of 200˜400 nm) andnear-infrared regions (i.e. at wavelengths of 700˜2500 nm) can be used.

Furthermore, since the polymer of the present invention has nofunctional groups (e.g., carboxyl and carbonyl groups), it has improvedheat resistance, moisture resistance, chemical resistance and flameretardancy. Carboxyl groups absorb light in the near-IR region, andcarbonyl groups absorb light in the UV region. The removal of suchfunctional groups is therefore advantageous in terms of inhibition ofoptical loss.

The copolymer prepared using the cyclic perfluoroalkyl vinyl ether ofthe present invention may be an amorphous polymer. One way to providesuch a polymer is by controlling the molar ratio between monomers used.The amorphous polymer inhibits optical loss due to light scattering.

Furthermore, since the polymer of the present invention may have a highmolecular weight, a T_(g) of 190° C. or higher and a thermaldecomposition initiation temperature of 270° C. or higher-made byappropriately controlling the composition of monomers—it can be usefullyapplied to an optical plastic material. For example, a terpolymerprepared from monomer 1 of Formula 2 or 3, monomer 2 of Formula 4, and atetrafluoroethylene monomer, has a low crystallinity, a high T_(g), andlittle or no optical loss even in long wavelength regions.

The present invention also provides an optical plastic materialcomprising (a) the perfluorinated polymer, and optionally (b) a dopantfor providing a refractive index gradient to the final material.Preferably, the dopant has a refractive index difference of 0.001 ormore from the perfluorinated polymer.

As noted above, since the polymer prepared by the process of the presentinvention is transparent over a very broad range of wavelengths, haslittle or no optical loss upon light penetration, is amorphous and hasexcellent heat resistance, it can be suitably used as a lighttransmission medium for optical devices. In particular, since thepolymer of the present invention has little optical loss even at longwavelengths as well as at short wavelengths and excellent thermalproperties, it can be advantageously used in the production of an SI orGI type plastic optical fiber.

The fabrication of a preform for an SI type plastic optical fiber or theproduction of an optical fiber by using the polymer of the presentinvention is possible by any known process. For example, a core isformed from the polymer of the present invention, and a clad is formedfrom another polymer for an optical fiber having a refractive indexdifferent from the polymer of the present invention, thereby obtaining astep refractive index gradient.

Meanwhile, when it is intended to produce a GI-type plastic opticalfiber or to fabricate a preform for an optical fiber, a dopant is usedfor providing a refractive index gradient to the final material.Examples of dopants that can be used in the present invention includeany those that can be used to produce a POF, e.g.,chlorotrifluoroethylene (CTFE), which has already been used to producean optical fiber using Cytop by professor Koike. The kind of dopants maybe properly selected by considering compatibility with the copolymer,non-volatility and refractive index. In addition, one must take intoaccount that the diffusion during perform fabrication and the separationof the fabricated preform are carried out at a temperature higher thanthe T_(g) of the copolymer.

Specific examples of dopants include perfluoro-fluorene,perfluorobenzyltetralini, poly(trifluoro-chloroethylene) oil,perfluoro-polyether oil (Krytox),1,1,3,5,6-pentachloro-nonafluorobenzene, etc. Perfluoro-polyether oiland perfluorobenzyltetralin are more preferred, andperfluorobenzyltetralin is most preferred. Since perfluorobenzyltetralinis a true solvent for the polymer of the present invention, thediffusion of the dopant becomes easier. Further, since the specificgravity of perfluorobenzyltetralin (2.049 g/cm³) is higher than that ofthe polymer of the present invention, the dopant is easily diffused intothe polymer in the molten state by centrifugal force, therebyfacilitating the formation of a refractive index gradient. Any knownmethod can be used to obtain a refractive index gradient by diffusing adopant into a polymer. A representative method is disclosed in JapanesePatent Laid-open No. Hei 8-334634. The content of a dopant in an opticalplastic material can be appropriately determined depending on differencebetween the refractive index of the polymer and that of the dopant, anda desired refractive index gradient.

The production of an optical plastic material, and particularly, thefabrication of a preform for a GI optical fiber, by using the polymer ofthe present invention are possible by all common processes. Thefollowing process is an example: the amorphous copolymer (a) of thepresent invention is molded to form a hallow in a reactor; the dopant(b) having a refractive index difference of at least 0.001 from thecopolymer (a) is added to the hallow; the reactor is rotated usingcentrifugal force at a high speed to diffuse the dopant (b) toward thecopolymer (a) in a molten state, thereby fabricating a preform for a GItype POF. Since the concentration of the dopant (b) having a relativelyhigh refractive index is higher at the central portion, the preform hasa refractive index profile in which the refractive index profiledecreases from the center to the peripheral surface.

The polymer prepared by the process of the present invention can besuitably used as a light transmission medium for optical devices such asPOFs, optical waveguides, optical decouplers, optical branching filters,optical switches, optical attenuators, optical isolators, opticalintegrated circuits, light transmitting/receiving modules and the like.The medium is excellent in terms of accessability to the above opticaldevices, low optical loss and high bandwidth. The GI-type POF producedby using the polymer of the present invention has little or no opticalloss, no variation in refractive index gradient depending on time andtemperature, and is thus highly stable. Accordingly, the GI type POFproduced by using the polymer of the present invention can beadvantageously used in various industrial fields, e.g., subscribercommunication lines, LANs for public facilities such as factories,hospitals and schools, power line monitoring communication lines, imagetransmission of monitored operation conditions of automobiles andsubways, internal communication of large ocean-going vessels, internaldata transmission of aircrafts, picture transmission requiring highspeed and high bandwidth in commercial game sets, transmission of highdefinition children's stories and 3-dimensional pictures, wires ofdevices such as computers or automatic switches, general indoorcommunication networks, various sensors and the like.

EXAMPLES

Hereinafter, the present invention will be described in more detail withreference to the following preferred examples. However, these examplesare given for the purpose of illustration and are not to be construed aslimiting the scope of the invention.

Synthesis of Monomers

1) Synthesis of FM 1:

As depicted in the reaction scheme below, hexafluoropropyleneoxide wasadded to a mixture of compound (I) (fluoroketone of perfluorocyclohexanecarboxylic acid) and diglyme (dimethylether of diethylene glycol) in aglass reactor at 0° C., and reacted to obtain compound (II) (b.p: 135°C.). The conversion rate of the compound (I) was 50%, and the yield ofthe compound (II) was 37%.

Na₂CO₃ and diglyme were added to a mixture containing the compound (II)and reacted at 50° C. The reaction mixture was heated to 120° C., andfurther reacted to give a reaction mixture containing monomer FM-1(conversion rate of compound (II): 100%):

The monomer FM-1 was separated from the reaction mixture at reducedpressure, washed with water to remove the diglyme, dried over calcinedmagnesium sulfate, and purified using a Perkin Elmer rectificationcolumn to give pure monomer FM-1 of the following formula (yield: 75%).

The monomer FM-1 was observed to have a boiling point of 122° C.

2) Synthesis of FM 1a:

The compound (II) and hexafluoropropyleneoxide were subjected tocondensation to give compound (III) of the following formula:

Similarly to the synthesis of FM-1, Na₂CO₃ and diglyme were added to thecompound (III) and reacted to obtain monomer FM-1a of the followingformula:

3) Synthesis of Monomer FM-2:

Monomer FM-2 was synthesized in accordance with the following reactionscheme:

In step 1, pentafluorophenylchloride and trifluoroacetic anhydride werereacted to obtain octafluoroacetophenone. In steps 2 and 3, theoctafluoroacetophenone was reacted with chloroethanol in hexane at−10˜−5° C. The reaction product was reacted with dry K₂CO₃ at 20° C. for6 hours to obtain 2-trifluoromethyl-2-pentafluorophenyl-1,3-dioxalane ina yield of 80%. In step 4, the fluoro-containing dioxalane waschlorinated with carbon tetrachloride at 50° C. to obtain2-trifluoromethyl-2-pentafluorophenyl-4,4,5,5,-tetrachloro-1,3-dioxalane(yield: 95%) as a colorless crystal. The product was measured to have amelting point of 41˜42° C. and a boiling point of 140˜141° C./40 mmHg.In step 5, the dioxalane obtained in step 4 was chlorinated withSbF₃/SbCl₅ at 120° C. for 2.5 hours to obtain a reaction mixturecontaining fluorinated dioxalane. The reaction mixture was subjected torectification to give2-trifluoromethyl-2-pentafluorophenyl-4,5-dichloro-4,5-difluoro-1,3-dioxalanein a yield of 70%. The analytical data of the NMR spectrum of theproduct are as follows:

NMR ¹⁹F (CH₃Cl) δ m.g.: −159.6, 159.3 (s) (F², 2F), −146.73 (F³, 2F),−135.98 (m) (F¹, 2F), −84.61, −84.16 (t), −67.54 (m), −65.74 (s),−58.67, −54.01 (m)

In step 6, the difluorinated derivative of dioxalane was dehalogenatedin N-methylpyrrolidone with the aid of Zn and ZnCl₂ at 90° C. to givemonomer FM-2.

In the IR spectrum, the monomer FM-2 had a carbon-carbon double bondband at 1885 cm⁻¹. The boiling point of the monomer FM-2 was measured tobe 86° C./38 mmHg.

4) Synthesis of FM-3:

As depicted in the following reaction scheme,3,6-perfluorodimethyl-1,4-dioxanyl-5-vinyl ether (hereinafter, referredto as ‘monomer FM-3’) was synthesized.

GC and NMR ¹⁹F analyses indicate that the monomer FM-3 has threeisomers. The boiling point of the monomer FM-3 was measured to be103˜105° C., the content of the major isomer in the monomer FM-3 wasshown to be 98%, and the yield of the monomer FM-3 was shown to be 80%.

Synthesis of Initiators

1) Synthesis of DAP-1

Bis-perfluorocyclohexanoylperoxide was synthesized in accordance withthe following reaction scheme:

The reaction was conducted in CF₂Cl—CF₂Cl (1,2dichloro-1,1,2,2-tetrafluoroethane: hereinafter, referred to as ‘R113’)at 10° C. Peroxide was separated from the aqueous layer, and dried overanhydrous sodium sulfate. The final yield was 90%. The obtained peroxidewas stored in a 10˜20% R113 solution.

The main characteristics of the bis-perfluorocyclohexanoylperoxide areshown in the following table:

NMR F¹⁹ Formula Molecular weight No. singlet T_(melting) ° C.

650 1, 52, 436 40.1 ~ 40.3

2) Synthesis of DAP-2

In order to obtain a perfluoroperoxide initiator which enablespolymerization around room temperature and introduction of the group—CF₂(CF₃)—O—CF— into a polymer backbone, hexafluoropropyleneoxide anddifluoroanhydride of octafluoroadipic acid (I) were subjected tocondensation to give a diacylpolyperfluoroperoxide initiator (DAP-2).The reaction scheme is as follows:

The characteristics of the peroxide are shown in the following table:

Half life τ (hrs) at T° C. Peroxide 30.0° C. 35.0° C. Yield (□) DAP-22.7 1.6 60

Preparation of Polymers

Using the polymerization devices shown in FIGS. 1 and 2,homopolymerization and copolymerization were performed.

The homopolymerization was performed in a 200 ml glass ampoule (FIG. 1),and the copolymerization of the monomer and tetrafluoroethylene wasperformed in a steel ampoule equipped with a mechanical agitator (FIG.2).

Radical polymerization was performed in R113 at 25˜60° C. in thepresence of DAP-1 or DAP-2 as an initiator. Oxygen in air was removedfrom the reaction medium at −196° C. The obtained polymer was separatedusing alcohol, centrifuged, and dried at 120° C. until the weight wasmaintained to be constant.

Hereinafter, the homopolymerization, the copolymerization and thecharacteristics of the obtained polymers will be described.

1) Homopolymerization of FM-1:

DAP 1 was used as an initiator, and the molar ratio of the monomer tothe initiator (FM-1:DAP-1) was controlled to 60:1. FM-1 was subjected tohomopolymerization for 5˜6 hours to give a homopolymer of FM-1. Theyield of the homopolymer was 20%, and the weight average molecularweight was measured to be 8,500. The homopolymer was transparent at 20°C.

2) Homopolymerization of FM-1a:

Homopolymerization of FM-1a was performed under the same polymerizationconditions as the homopolymerization of FM-1 to give a homopolymer ofFM-1a. The yield of the homopolymer was 15%. The homopolymer was shownto have a low molecular weight. The homopolymer was in the form of aviscous gel at 20° C.

3) Homopolymerization of FM-3:

Homopolymerization of FM-3 was performed under the same polymerizationconditions as the homopolymerization of FM-1 to give a homopolymer ofFM-3. The yield of the homopolymer was 14%. The homopolymer wascompletely amorphous in the form of a transparent jelly.

4) Copolymerization of FM-1 and Tetrafluoroethylene (HereinafterReferred to as ‘TFE’):

Copolymerization was performed in R113 at 2.5 atm and 60° C. for 2 hoursin the presence of DAP-1 as an initiator. The molar ratio of the totalmonomers to the initiator ((FM-1+TFE):DAP-1) was controlled to 190:1,and the molar ratio of FM-1 to TFE was controlled to 65:35. The yield ofthe copolymer was 80%. The copolymer was in the form of a solid lightpowder, and was measured to have a molecular weight 10˜100 times higherthan that of the homopolymer of FM-1. The copolymer contained 5% or morecrystalline region. As the molar fraction of TFE was increased, thecrystalline region (%) was increased. The copolymer was measured to havea boiling point of 200° C., and a thermal decomposition initiationtemperature of 270° C.

5) Copolymerization of FM-1a and TFE:

A copolymer (yield: 70%) of FM-1a and TFE was prepared in the samemanner as in 4) above, except that the molar ratio of the total monomersto the initiator (FM-1a+TFE):DAP-1 was changed to 190:1, and the molarratio of the FM-1a to TFE was changed to 65:35. The copolymer containeda slightly crystalline phase.

6) Copolymerization of FM-3 and TFE:

A copolymer (yield: 35%) of FM-3 and TFE was prepared in the same manneras in 4) above, except that the molar ratio of the total monomers to theinitiator (FM-3+TFE):DAP-1 was changed to 190:1, and the molar ratio ofthe FM-3 to TFE was changed to 65:35. The copolymer was in the form of asolid and contained a minimal crystalline phase. The T_(g) was measuredto be 192° C.

7) Terpolymer of FM-1, FM-3 and TFE:

DAP-2 was used as an initiator, the molar ratio of the total monomers tothe initiator was 190:1, the molar ratio between the monomers(FM-1:FM-3:TFE) was 4:4:2, and copolymerization was performed at 25° C.for 2 hours. The yield of the terpolymer was 52%. The terpolymercontained a minimal crystalline phase. The terpolymer had a T_(g) of172° C.

Fabrication of Preform 1 for GI Type POF

50 g of the copolymer prepared in 4) above was charged into a glass tube(diameter: 4 cm), and rotated in the vertical position at a rate of6,000 rpm and 270° C. for 6 hours to form a hallow in the tube.Perfluorobenzyltetralin (25 wt %) as a dopant was filled into the hallowand rotated in the vertical position at a rate of 4,000 rpm and 200˜220°C. for 8 hours. At this time, the dopant was diffused into the copolymerdue to a difference between the specific gravity of the dopant and thatof the copolymer to form a refractive index gradient. The resultingpreform was cooled to room temperature to fabricate a final preform(diameter: 4 cm) for a GI type plastic optical fiber. The differencebetween the refractive index of the central portion and that of theperipheral surface was confirmed to be 0.01.

Fabrication of Preform 2 for GI Type POF

50 g of the copolymer prepared in 5) above was charged into a glass tube(diameter: 4 cm), and rotated in the vertical position at a rate of5,000 rpm and 270° C. for 5 hours to form a hallow in the tube.Perfluorobenzyltetralin (25 wt %) as a dopant was filled into the hallowand rotated in the vertical position at a rate of 4,000 rpm and 200˜220°C. for 7 hours. At this time, the dopant was diffused into the copolymerdue to a difference between the specific gravity of the dopant and thatof the copolymer to form a refractive index gradient. The resultingpreform was cooled to room temperature to fabricate a final preform(diameter: 4 cm) for a GI type plastic optical fiber. The differencebetween the refractive index of the central portion and that of theperipheral surface was confirmed to be 0.015.

Fabrication of Preform 3 for GI Type POF

50 g of the copolymer prepared in 6) above was charged into a glass tube(diameter: 4 cm), and rotated in the vertical position at a rate of6,000 rpm and 270° C. for 5 hours to form a hallow in the tube.Perfluorobenzyltetralin (25 wt %) as a dopant was filled into the hallowand rotated in the vertical position at a rate of 4,000 rpm and 200˜220°C. for 7 hours. At this time, the dopant was diffused into the copolymerdue to a difference between the specific gravity of the dopant and thatof the copolymer to form a refractive index gradient. The resultingpreform was cooled to room temperature to fabricate a final preform(diameter: 4 cm) for a GI type plastic optical fiber. The differencebetween the refractive index of the central portion and that of theperipheral surface was confirmed to be 0.015.

Fabrication of Preform 4 for GI Type POF

50 g of the copolymer prepared in 7) above was charged into a glass tube(diameter: 4 cm), and rotated in the vertical position at a rate of6,000 rpm and 270° C. for 5 hours to form a hallow in the tube.Perfluorobenzyltetralin (25 wt %) as a dopant was filled into the hallowand rotated in the vertical position at a rate of 4,000 rpm and 200˜220°C. for 7 hours. At this time, the dopant was diffused into the copolymerdue to a difference between the specific gravity of the dopant and thatof the copolymer to form a refractive index gradient. The resultingpreform was cooled to room temperature to fabricate a final preform(diameter: 4 cm) for a GI type plastic optical fiber. The differencebetween the refractive index of the central portion and that of theperipheral surface was confirmed to be 0.017.

Measurement of Refractive Index Gradients:

The refractive index gradient of the preforms 1 to 4 fabricated abovewas measured in accordance with the following procedure. The results aresummarized in Table 1 below.

1) Method: Confocal Raman spectroscopy

2) A 20 mW helium-neon laser (632.8 nm) was used. The Raman scatteringspectroscopy shows the results measured using an Olympus BH microscopewhen pinholes were set to 50 μm.

According to how parabolic the refractive index of the preforms waschanged toward the peripheral surface, the most parabolic form wasjudged to be “excellent”, and the relatively parabolic form was judgedto be “good”.

TABLE 1 Degree of Dopant Diffusion Diffusion Average T_(g) refractiveindex Preform content time temp. of Preform gradient of for POF (wt %)(hr) (° C.) (° C.) preform 1 25 8 200-220 120 Excellent 2 25 7 200-220121 Good 3 25 7 200-220 110 Good 4 25 7 200-220 130 Good

The refractive index gradient of the preform 1 for an optical fiber isshown in FIG. 3. As can be seen from FIG. 3, the refractive indexgradient of the preform is parabolic.

As apparent from the above description, the polymer prepared by thecopolymerization of the cyclic perfluoroalkyl vinyl ether of the presentinvention has a high molecular weight, is substantially transparent inthe UV and near IR regions, and can be completely amorphous bycontrolling the molar ratio between monomers. Accordingly, the copolymerof the present invention can be usefully applied to an optical plasticmaterial. In particular, the preform for a GI-type plastic optical fiberfabricated by using the copolymer of the present invention has a highT_(g), a parabolic refractive index profile, superior thermal stabilityand little or no optical loss.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

1-2. (canceled)
 3. A process for preparing a fluorinated polymer bycopolymerizing a perfluoroalkyl vinyl ether represented by Formula 1below:

wherein RF is a fluorine atom or a C_(1˜5) perfluoroalkyl group; A is asingle bond, —(CF₂)_(n)— in which n is an integer of 1 to 5, or—(CF₂CR^(F) ₂—O—CF₂)— in which the substituents R^(F) are eachindependently a fluorine atom or a C_(1˜5) perfluoroalkyl group;

 is a perfluoro cyclohexyl, perfluorophenyl, perfluorodioxanyl orperfluorodioxalanyl group, and a perfluorinated olefin monomer in achlorofluorinated solvent in the presence of a perfluorinated radicalinitiator.
 4. The process according to claim 3, wherein theperfluoroalkyl vinyl ether and the perfluorinated olefin monomer arecopolymerized with a fluorinated monomer represented by Formula 5 below:

wherein RF is a fluorine atom or a C_(1˜5) perfluoroalkyl group; and

 is a perfluoro cyclohexyl, perfluorophenyl, perfluorodioxanyl orperfluorodioxalanyl group.
 5. The process according to claim 3, whereinthe cyclic perfluoroalkyl vinyl ether (A) of Formula 1 and theperfluorinated olefin monomer (B) is copolymerized in a molar ratio(A:B) between 99:1 and 50:50.
 6. The process according to claim 3,wherein the perfluoroalkyl vinyl ether compound is a compoundrepresented by any one of Formulae 2 to 4 below:

and the perfluorinated olefin monomer is tetrafluoroethylene orhexafluoropropylene.
 7. The process according to claim 3, wherein theperfluorinated radical initiator is a perfluorinated peroxide compound.8. The process according to claim 7, wherein the perfluorinated radicalinitiator is bis-perfluorocyclohexyl-peroxide of Formula 6 below, apolyperfluoroperoxide represented by Formula 7 below or a mixturethereof:

wherein n is an integer between 1 and 10, and m is an integer between 1and
 40. 9. A polymer prepared by the process according to claim
 8. 10.An optical plastic material comprising the polymer according to claim 9.11. The optical plastic material according to claim 10, furthercomprising a dopant having a refractive index difference of 0.001 ormore from the polymer.
 12. The optical plastic material according toclaim 11, wherein the dopant is selected from the group consisting ofperfluorofluorene, perfluorobenzyltetralin,poly(trifluoro-chloroethylene) oil, perfluoro-polyether oil (Krytox) and1,1,3,5,6-pentachloro-nonafluorobenzene.
 13. The optical plasticmaterial according to claim 10, wherein the polymer is used to produce astep refractive index type optical fiber, a rod lens, an opticalwaveguide, an optical decoupler, a wavelength multiplexer and wavelengthdemultiplexer, an optical attenuator, an optical switch, an opticalisolator, a light transmitting module, a light receiving module, acoupler, an optical detector or an optical integrated circuit.
 14. Apreform for an optical fiber fabricated from the optical plasticmaterial according to claim
 10. 15. An optical fiber produced from thepreform according to claim
 14. 16. A polymer prepared by the processaccording to claim
 4. 17. A polymer prepared by the process according toclaim
 5. 18. A polymer prepared by the process according to claim
 6. 19.A polymer prepared by the process according to claim
 7. 20. A polymerprepared by the process according to claim
 8. 21. A preform for anoptical fiber fabricated from the optical plastic material according toclaim
 11. 22. An optical fiber produced from the preform according toclaim 21.